1. Field of the Invention
The present invention relates to electron flood apparatuses and ion implantation systems.
2. Related Background Art
Ion implantation systems are used for introducing dopant into substrates. In an ion implantation process, positive charge accumulates on the surface of the insulating layer of the substrate because the ions implanted onto the substrate are usually cations. If the voltage applied to the insulating layer by means of the accumulated charge exceeds a dielectric breakdown voltage, the device may be damaged.
Typically, an ion implantation system comprises an electron flood apparatus for supplying electrons to neutralize the accumulated charge on the substrate. As electron flood apparatuses, for example, an electron flood apparatus comprising filaments such as tungsten is known.
However, there are problems with an electron flood apparatus using filaments, such as contamination due to foreign matter from the filaments, or life
This application claims priority to Japan Application Serial No. 2003-328800, filed Sep. 19, 2003. shortening of the filaments. Accordingly, electron flood apparatuses referred to as plasma flood systems or the like are known as electron flood apparatuses for solving these problems (see, for example, Japanese Patent Application Laid-Open No. 11-73908).
FIG. 8 is a cross-sectional view of an electron flood apparatus referred to as a plasma flood system or the like. This electron flood apparatus comprises an insulative chamber 155 and an electrode 215 provided in the chamber 155. The chamber 155 is made of, for example, alumina, quartz, BN, sapphire or the like. The chamber 155 has an opening 165. The opening 165 is in communication with an opening 145 provided in a side wall of a tube 135 through which an ion beam 185 passes.
Ar gas is supplied from a supply port 175 into the chamber 155. The outer circumference of the chamber 155 is wrapped with a coil 185, which is connected to an RF power source 195 via an impedance matching circuit 205. Plasma of Ar gas is generated in the chamber 155 by RF electric power supplied from the RF power source 195. Here, if voltage is applied to the electrode 215 by means of the power source 225, electrons contained in the plasma are supplied into the tube 135 from the opening 165.